Electric heating unit



C. C. ABBOTT.

ELECTRIC HEATING UNIT. APPLICATION FILED OCT. 30. 1919.

Patented Oct. 25, 1921.

Fig.1. ,3

Inventor: Charles C. bbott,

His flttorneg.

UNITED STATES PATENT OFFICE.

C. ABBOTT, OF PITTSFIELD, MASSACHUSETTS, AS SIGNOR TO GENERAL ELEC- TRIOCOMPANY, A CORPORATION OF NEW YORK.

nmio'rnrc HEATING um'r.

Specification of Letters Patent.

Patented Oct. 25, 1921.

Application filed'october 30, 1919. Serial No. 334,454.

Massachusetts, have invented certain newand useful Improvements inElectric Heatmg Units, of which the following is a specification.

My invention relates to electric heating elements of the type in whichconductors are inclosed in a metallic sheath and insulated therefrom bya thin dense layer of insulating material having relatively high heat.conducting properties. In my pending application for patent, Serial No.262,722, filed November 15, 1918, I disclosed a heating element of thisgeneral character and my present invention is in the nature of animprovement upon that device. In said application, a device is shownhaving a metallic sheath filled with a dense mass of refractoryinsulating material and a single helical or sinuous conductor embeddedin said mass. Obviously, with such a device, but one de gree of heat isobtainable with a constant current. One of the objects of my presentinvention is to provide a heating unit of the character .described inwhich difierent degrees of heat may be obtained, such as low,

80 medium and maximum, with a constant current. This I accomplish byproviding a plurality of helical or sinuous conductors in saidunit andconnecting said conductors in difierent combinations by any suitable 85switch. For example, in a two coil unit, said coils are connected inseries for low heat, and in parallel for the maximum orhigh heat. Asingle coil may be used for medium heat. By such an arrangement a betterheat regulation is possible. This device could be readily used inconnection with a thermostatically controlled switch where it is desiredto automatically control the temperature.

Further objects of my invention will appear from the following detaileddescription when taken in connection with the accompanying drawings, inwhich Figurel is a longitudinal section of one form of my invention;Fig. 2 is a view of the terminal end; Fig. 3 is a' section taken on theline I-1 of Fig. 1; Fig. 4 is a section taken on .the line 2-2 of Fig.1; and Fig. 5 is a perspective View of one form of lava spacer employedin my invention.

Referring tothe drawings, 1 is a metal core, preferably of extrudedbrass, which is cross-shaped as shown in Fig. 3. This core is insertedin a sheath 2, which is made from any, suitable metal capable of beingswaged or drawn down, such as steel. This sheath .is somewhat longerthan said core so that other additional necessary members may beaccommodated therein. The core 1, which is spun out at one end, isdriven into said sheath, preferably from the terminal end 3, so as totightly fit therein. Before the core has thus been fitted -.into thesheath the latter member is counter-bored and chamfered at the end 3 inorder that this end may be more readily spun over. Alava spacer 4, aninsulating washer 5, preferably mica, and a metallic disk 6, are nextplaced in the end 3 in the order named. 'The spacer 4, washer 5 and disk6 are provided with openings through which the resistor terminals maypass. The number of openings of course' depends upon the number ofterminals used. In the preferred form, however, four terminals are usedand 'four openings 7, 8, 9 and 10 are provided. I have also providedanother small opening 11 in these units, and a hole 12 in the core 1.. Adowel pin is driven through the openings 11 into the hole 12 to keep theopenings 7, 8, 9 and 10 of the units 4, 5 and 6 in register,

while the heating unit is being assembled.

After the parts 4,5 and 6 have been thus placed in the sheath 2,"the end3 is spun over. A lava spacer 13 is next placed in the other end of thetube 2, adjacent the core 1, which is provided with a number of openings7', 8', 9' and 10', corresponding to those in the spacer 4. The spacer'13 is also providedwith a tongue 14 which'fits into a groove 15 of thecore 1, to hold the spacer in position while the unit is beingassembled, and to keep the holes 7', 8', 9' and 10' in register with iheholes 7, 8, 9 and 10. The spacer 13 is a so provided with a diametricalslot 16 connectin the-holes 8' and 10 as shown in Fig. 5. 1 indicates ahelicalresistance element which is made of a high resistance material,such as nickel-chromium alloy. This element has been cut the properlength, and its ends are suitably secured to terminal pins 18 and 19passed through the 9 respectively. The sheath 2 is then filled metallicsheath and a with an insulating powder 23, such as magnesia, so as tocompletely embed the resistance elements 17 and 20. After the sheath hasbeen thus filled, the end 24 whichis also slightly counterbored, isclosed with a metallic disk 25. The edge of the sheath 2 is slightlyprick-punched over to hold the disk 25 in position while the unit isbeing swaged. The unit is now subjected to a reducing process whichconsists in passing it through a swaging or rolling machine. After theunit has been swaged, the disk 25 is welded to the sheath 2 so as tomake a waterproof joint.

While I have described my invention as embodied in concrete formfand asoperating in a specific manner in accordance with the provisions of thepatent statutes, it should be understood that I do not lim t myinvention thereto, since various modifications will suggest themselvesto those skilled in the art without departing from the spirit of myinvention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. An electric heating unit comprisin a metallic sheath and a pluralityof helical resistance elements embedded in pulverulent heat-refractoryinsulating material compacted to a dense mass around said elementsWithin the sheath.

2. An electric heating unit comprising a metallic sheath and a pluralityof helical resistance elements embedded in pulverulent heat-refractoryinsulating material compacted to a dense mass around said elementswithin the sheath, and terminal members for said elements projectingfrom the sheath.

3. An electric heating unit comprising a plurality of helical reslstanceelements, each of which is doubled forming parallel spirals with itsterminals at the same end, embedded in a pulverulent heatmefractoryinsulating material compacted to a dense mass around said elementswithin the sheath.

4. An electric heating unit comprising a metallic sheath, a plurality ofhelical resistance elements embedded in pulverulent heat-refractoryinsulating material compacted to a dense mass around said elementswithin the sheath and terminal members with threaded ends screwed intothe spirals with their opposite ends projecting from the sheath.

5. An electric heating'unit comprising a metallic sheath and a pluralityof helical resistance elements, each of which is doubled formingparallel helices with its terminals at the same end, embedded in apulverulent heat-refractory insulating material compacted to a densemass within said sheath, and terminal pins with threaded ends screwedinto the helical ends of said elements with their opposite endsprojectlng from said sheath.

6. An electric heating unit comprising a metallic sheath, a metal coretherein pro-- vided with longitudinal openings, and a plurality ofhelical resistance elements emedded in pulverulent heat-refractoryinsulating material compacted to a hard dense mass in said longitudinalopenings.

7. An electric heating unit comprising a metallic sheath, a cross-shapedcore therein, two spiral resistance elements each of which is doubledforming parallel spirals in the openings of said core and a pulverulentheat-refractory insulating material compacted to a hard dense massaround said elements. 1

8. An electric heating unit comprising a metallic sheath and a helicalresistance element, which is doubled forming parallel helices with itsterminals at the same end, embedded in a pulverulent heat-refractoryinsulating material compacted to a dense mass around said element withinthe sheath.

9. An electric heating unit comprising a metallic. sheath, across-shaped core therein and a plurality of helical resistance elementsembedded in pulverulent heat-refractory insulating material compacted toa hard dense mass in the openings formed by the crossshaped core.

10. An electric heating unit comprising a metallic sheath, a metal coretherein provided with longitudinal openings, a plurality of helicalresistance elements embedded in pulverulent heat-refractory insulatingmaterial compacted to a hard dense mass in said longitudinal openingsand terminal members with threaded ends screwed into the helices Withtheir opposite ends projecting from the sheath.

11. An electric heatingunit comprising a metallicsheath, a cross-shapedcore therein, a plurality of helical resistance elements embedded inpulverulent heat-refractory insulating material compacted to a harddense mass in the openings formed by the crossshaped core and terminalmembers with threaded ends screwed into the helices with their oppositeends projecting from the sheath.

12. An electric heating unit comprising a metallic sheath, across-shaped core therein, an insulating spacer adjacent said core, two

helical resistance elements in the longitudinal openings formed by saidcross-shaped core bent over said spacer and held out of contact witheach other by it, a pulverulent heat-refractory insulating materialsurrounding said elements and compacted to a hard dense mass andterminal members with 10 threaded ends screwed into the helical ends ofsaid elements with their opposite ends projecting from the sheath.

In witness whereof, I have hereunto set my hand this 28th day ofOctober, 1919.

CHARLES C. ABBOTT.

